1. Field of the Invention
The present invention relates to the process of reducing the absorbable organic halogen (AOX) level in wet-strength resins while maintaining or improving their wet-strength effectiveness and more particularly it relates to treating such resins with base.
2. Description of the Prior Art
Commercial polyaminopolyamide-epichlorohydrin resins typically contain 1-10% (dry basis) of the epichlorohydrin (epi) by-products, 1,3-dichloropropanol (1,3-DCP), 2,3-dichloropropanol (2,3-DCP) and 3-chloropropanediol (3-CPD). Production of wet-strength resins with reduced levels of epi by-products has been the subject of much investigation. Environmental pressures to produce wet-strength resins with lower levels of absorbable organic halogen (AOX) species have been increasing. xe2x80x9cAOXxe2x80x9d refers to the absorbable organic halogen content of the wet strength resin which can be determined by means of adsorption unto carbon. Accordingly, AOX includes epichlorohydrin (epi) and epi by-products (1,3-dichloropropanol, 2,3-dichloropropanol and 3-chloropropanediol) as well as organic halogen bound to the polymer backbone.
Azetidinium-containing, polyaminopolyamide-epi resins have been treated with a basic ion exchange column to give a low AOX and low total chloride resin (WO/92/22601, assigned to Akzo NV). After this treatment, the resin was acidified. A disadvantage of this process is the ion exchange column has limited capacity and needs to be regenerated once the basicity is consumed. An additional disadvantage is the resin has reduced effectiveness when treated with the basic ion exchange column.
Other technologies remove epi by-products but do not remove polymer-bound AOX (i.e., polymeric aminochlorohydrin). Polyaminopolyamide-epi resins have been treated with microorganisms to reduce epi by-products to less than 10 ppm (EP 510987, assigned to Hercules Incorporated). This treatment, however, does not remove organic halogen bound to the polymer backbone. Another process to remove epi by-products uses a column of carbon adsorbent (WO 93/21384, assigned to E. I. duPont de Nemours). Such columns have limited capacity and to need to be regenerated once the adsorbent no longer efficiently removes the epi by-products.
According to the present invention there is provided a process for reducing the AOX content of a starting water-soluble wet-strength resin comprising azetidinium ions and tertiary aminohalohydrin, comprising treating said resin in aqueous solution with base to form treated resin, wherein at least about 20% of the tertiary aminohalohydrin present in the starting resin is converted into epoxide and the level of azetidinium ion is substantially unchanged, and the effectiveness of the treated resin in imparting wet strength is at least about as great as that of said starting wet-strength resin.
Further provided is the water-soluble wet-strength resin prepared by the process of the present invention.
Still further provided is the process for preparing paper using the wet-strength resin prepared by the present invention and the paper so made.
It surprisingly has been discovered that the AOX content of azetidinium and aminochlorohydrin containing wet strength resins can be greatly reduced while maintaining or even improving their wet strength characteristics. The starting water-soluble wet-strength resins of the present invention can be polyaminopolyamide-epi resins or polyalkylene polyamine-epi resins and mixtures thereof.
The conversion of the tertiary aminochlorohydrin (ACH) of the wet-strength resins of the present invention to tertiary epoxide by base treatment can be illustrated by the following formula: 
Polyaminopolyamide-epichlorohydrin resins comprise the water-soluble polymeric reaction product of epichlorohydrin and polyamide derived from polyalkylene polyamine and saturated aliphatic dibasic carboxylic acid containing from about 3 to about 10 carbon atoms. It has been found that resins of this type impart wet-strength to paper whether made under acidic, alkaline or neutral conditions. Moreover, such resins are substantive to cellulosic fibers so that they may be economically applied thereto while the fibers are in dilute aqueous suspensions of the consistency used in paper mills.
In the preparation of the cationic resins contemplated for use herein, the dibasic carboxylic acid is first reacted with the polyalkylene polyamine, under conditions such as to produce a water-soluble polyamide containing the recurring groups
xe2x80x94NH(CnH2nNH)xxe2x80x94CORCOxe2x80x94
where n and x are each 2 or more and R is the divalent hydrocarbon radical of the dibasic carboxylic acid. This water soluble polyamide is then reacted with epi to form the water-soluble cationic thermosetting resins.
The dicarboxylic acids contemplated for use in preparing the resins of the invention are the saturated aliphatic dibasic carboxylic acids containing from 3 to 10 carbon atoms such as succinic, glutaric, adipic, azelaic and the like. The saturated dibasic acids having from 4 to 8 carbon atoms in the molecule, such as adipic and glutaric acids are preferred. Blends of two or more of the saturated dibasic carboxylic acids may also be used.
A variety of polyalkylene polyamines including polyethylene polyamines, polypropylene polyamines, polybutylene polyamines, polypentylene polyamines, polyhexylene polyamines and so on and their mixtures may be employed of which the polyethylene polyamines represent an economically preferred class. More specifically, the polyalkylene polyamines contemplated for use may be represented as polyamines in which the nitrogen atoms are linked together by groups of the formula xe2x80x94Cn H2nxe2x80x94where n is a small integer greater than unity and the number of such groups in the molecule ranges from two up to about eight. The nitrogen atoms may be attached to adjacent carbon atoms in the group xe2x80x94Cn H2nxe2x80x94or to carbon atoms further apart, but not to the same carbon atom. This invention contemplates not only the use of such polyamines as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and dipropylenetriamine, which can be obtained in reasonably pure form, but also mixtures and various crude polyamine materials. For example, the mixture of polyethylene polyamines obtained by the reaction of ammonia and ethylene dichloride, refined only to the extent of removal of chlorides, water, excess ammonia, and ethylenediamine, is a satisfactory starting material. The term xe2x80x9cpolyalkylene polyaminexe2x80x9d employed in the claims, therefore, refers to and includes any of the polyalkylene polyamines referred to above or to a mixture of such polyalkylene polyamines and derivatives thereof.
It is desirable, in some cases, to increase the spacing of secondary amino groups on the polyamide molecule in order to change the reactivity of the polyamide-epichlorohydrin complex. This can be accomplished by substituting a diamine such as ethylenediamine, propylenediamine, hexamethylenediamine and the like for a portion of the polyalkylene polyamine. For this purpose, up to about 80% of the polyalkylene polyamine may be replaced by molecularly equivalent amount of the diamine. Usually, a replacement of about 50% or less will serve the purpose.
In converting the polyamide, formed as above described, to a cationic thermosetting resin, it is reacted with epichlorohydrin at a temperature from about 25xc2x0 C., to about 100xc2x0 C. and preferably between about 35xc2x0 C. to about 70xc2x0 C. until the viscosity of a 20% solids solution at 25xc2x0 C. has reached about C or higher on the Gardner Holdt scale. This reaction is preferably carried out in aqueous solution to moderate the reaction. Although not necessary, pH adjustment can be done to increase or decrease the rate of crosslinking.
When the desired viscosity is reached, sufficient water is then added to adjust the solids content of the resin solution to the desired amount, i.e., about 15% more or less, the product cooled to about 25xc2x0 C. and then stabilized by adding sufficient acid to reduce the pH at least to about 6 and preferably to about 5. Any suitable acid such as hydrochloric, sulfuric, nitric, formic, phosphoric and acetic acid may be used to stabilize the product. However, hydrochloric acid and sulfuric acid are preferred.
In the polyamide-epichlorohydrin reaction, it is preferred to use sufficient epichlorohydrin to convert most of the secondary amine groups to tertiary amine groups. However, more or less may be added to moderate or increase reaction rates. In general, satisfactory results may be obtained utilizing from about 0.5 mole to about 1.8 moles of epichlorohydrin for each secondary amine group of the polyamide. It is preferred to utilize from about 0.6 mole to about 1.5 moles for each secondary amine group of the polyamide.
Epichlorohydrin is the preferred epihalohydrin for use in the present invention. The present application refers to epichlorohydrin specifically in certain instances, however, the person skilled in the art will recognize that these teachings apply to epihalohydrin in general.
Cationic water-soluble resins, derived from the reaction of epihalohydrins, such as epichlorohydrin, and polyalkylene polyamines, such as ethylenediamine (EDA), bis-hexamethylenetriamine (BHMT) and hexamethylenediamine (HMDA) have long been known. These polyalkylene polyamine-epihalohydrin resins are described in patents such as U.S. Pat. No. 3,655,506 to J. M. Baggett, et al. and others such as U.S. Pat. No. 3,248,353 and U.S. Pat. No. 2,595,935 to Daniel et al. from which their generic description as xe2x80x9cDaniel""s Resinsxe2x80x9d arises.
The polyalkylene polyamine employed in the present invention is selected from the group consisting of polyalkylene polyamines of the formula:
H2Nxe2x80x94[CHZxe2x80x94(CH2)nxe2x80x94NRxe2x80x94]xxe2x80x94H
where:
n=1-7,
x=1-6
R=H or CH2Y,
Z=H or CH3, and
Y=CH2Z, H, NH2, or CH3,
polyalkylene polyamines of the formula:
H2Nxe2x80x94[CH2xe2x80x94(CHZ)mxe2x80x94(CH2)nxe2x80x94NRxe2x80x94]xxe2x80x94H
where:
m=1-6, n=1-6, and m+n=2-7,
R=H or CH2Y,
Z=H or CH3, and
Y=CH2Z, H, NH2, or CH3, and mixtures thereof.
Polyalkylene polyamine-epihalohydrin resins comprise the water-soluble polymeric reaction product of epihalohydrin and polyalkylene polyamine. In making Daniel""s Resins the polyalkylene polyamine is added to an aqueous mixture of the epihalohydrin so that during the addition the temperature of the mixture does not exceed 60xc2x0 C. Lower temperatures lead to further improvements, though too low a temperature may build dangerously latent reactivity into the system. The preferred temperatures fall within the range of about 25xc2x0 C. to about 60xc2x0 C. More preferred is a range of from about 30xc2x0 C. to about 450xc2x0 C.
Alkylation of the polyamine occurs rapidly proceeding to form secondary and tertiary amines depending on the relative amounts of epihalohydrin and polyamine. The levels of epihalohydrin and polyamine are such that between about 50 and 100% of the available amine nitrogen sites are alkylated to tertiary amines. Preferred levels are between about 50 and about 80% alkylation of the amine nitrogen sites. Excess epihalohydrin beyond that required to fully alkylate all the amine sites to the tertiary amine is less preferred because this results in increased production of epihalohydrin byproducts.
To minimize epi byproducts and AOX, preferably time spent combining the polyamine and epichlorohydrin should be minimized. This is required to minimize the period during the combining of reactants, in which there is a significant level of unalkylated or partially alkylated polyamine in the presence of uncombined epichlorohydrin. This condition results in an alkaline system in which conversion to epihalohydrin by-products is accelerated. Through experience, it has been found that the time for addition of at least about 90% by weight of the polyamine, while maintaining the reaction temperature within the specified range, should not exceed 150 minutes if 1,3-DCP levels are to be kept below the maximum levels desired. A more preferred addition time is 120 minutes or less for addition of at least about 90% of the amine, with 100 minutes or less time of addition being most preferred. Once about 90% of the polyamine is added then the time of addition of the remainder becomes less important. This condition is specifically related to the completion of the alkylation reaction between the polyamine and the epihalohydrin, at which point practically all of the epihalohydrin has been consumed in alkylating the polyamine.
Following complete addition of the polyamine, the temperature of the mixture is allowed to rise and /or the mixture is heated to effect crosslinking and azetidinium formation. The crosslinking rate is a function of concentration, temperature, agitation, and the addition conditions of the polyamine all of which can be readily determined by those skilled in the art. The crosslinking rate can be accelerated by the addition of small shots of the polyamine or other polyamines of the present invention or addition of various alkalies at or near the crosslinking temperature.
The resin is stabilized against further crosslinking to gelation by addition of acid, dilution by water, or a combination of both. Acidification to pH 5.0 or less is generally adequate.
The preferred polyamines are bishexamethylenetriamine, hexamethylenediamine, and their mixtures.
A wide range of aminochlorohydrin (ACH) and azetidinium (AZE) levels is possible with polyaminopolyamide-epi and polyamine-epi resins and is suitable for use in this invention. The ratio of ACH:AZE is at least about 2:98, preferably at least about 5:95 and most preferably at least about 10:90. The ACH:AZE ratio can be up to about 98:2, preferably up to about 95:5 and most preferably up to about 90:10. The starting water-soluble wet-strength resins of the present invention always contain tertiary ACH. Optionally, they may additionally contain secondary ACH and/or quaternary ammonium chlorohydrin also.
The following structures illustrate functionalities referred to in the present application. The ACH, epoxide, glycol and amine crosslinking functionalities are illustrated in terms of their tertiary species. 
By the process of the present invention generally at least about 20% of the aminochlorohydrin present in the starting resin has been converted into epoxide. Preferably at least about 50% and most preferably at least about 90% of the aminochlorohydrin present in the starting resin has been converted to epoxide. By the present invention up to about 100% of the aminochlorohydrin present in the starting resin can be converted to epoxide.
It should be understood that the phrase xe2x80x9caminohalohydrinxe2x80x9d as used in the present application can refer to secondary aminohalohydrin, tertiary aminohalohydrin and quaternary ammonium halohydrin unless otherwise specified.
It should also be understood that the phrase xe2x80x9cepoxidexe2x80x9d and xe2x80x9caminoepoxidexe2x80x9d are used interchangeably in the present application and they refer to secondary am inoepoxide, tertiary am inoepoxide and quaternary aminionium epoxide unless otherwise specified.
Both organic and inorganic bases can be used herein in the present invention. A base is defined as any proton acceptor (see Advanced Organic Chemistry, Third Ed.; Jerry March; John Wiley and Sons: New York, 1985, p 218-236, incorporated herein by reference.) Typical bases include alkali metal hydroxides, carbonates and bicarbonates, alkaline earth metal hydroxides, trialkylamines, tetraalkylammonium hydroxides, ammonia, organic amines, alkali metal sulfides, alkaline earth sulfides, alkali metal alkoxides and alkaline earth alkoxides. Preferably, the base will be alkali metal hydroxides (lithium hydroxide, sodium hydroxide and potassium hydroxide) or alkali metal carbonates (sodium carbonate and potassium carbonate). Most preferably, the base is sodium hydroxide or potassium hydroxide.
The amount of base varies widely from resin to resin and is dependent on the resin type, the amount and type of polymeric aminochlorohydrin, the amount of the epi by-products (1,3-dichloropropanol, 2,3dichloropropanol and 3-chloropropanediol), the amount of stabilization acid in the resin and on the conditions used to activate the resin. The amount of base can be at least about 0.5 mmole, preferably at least about 1.5 mmole per dry gram of resin. The amount of base can be up to about 10 mmole, preferably up to about 8 mmole per dry gram of resin. The pH can be from 13.0-8.0, preferably 12.5-9.0, more preferably 12.0-10.0, most preferably 11.5-10.5.
The treatment temperature can be at least about 0xc2x0 C., preferably at least about 20xc2x0 C., preferably at least about 40xc2x0 C., more preferably at least about 45xc2x0 C. and most preferably at least about 50xc2x0 C. The treatment temperature can be up to about 100xc2x0 C., preferably up to about 80xc2x0 C. and most preferably up to about 60xc2x0 C. The treatment time can be at least about 1 minute, preferably at least about 3 min, and most preferably at least about 5 min. The treatment time can be up to about 24 hours, preferably up to about 4 hours and most preferably up to about 1 hour. The resin can be used about 1 minute to about 24 hours after base treatment, preferably about 1 minute to about 6 hours, most preferably about 1 minute to about 1 hour.
The resin solids for base treatment can be at least about 1%, preferably at least about 2%, preferably at least about 6%, more preferably at least about 8% and most preferably at least about 10% based upon the weight of the composition. In the context of the present invention the phrase xe2x80x9cresin solidsxe2x80x9d means the active polyaminopolyamide-epi and/or polyalkylene polyamine-epi of the composition. The resin solids for base treatment can be up to about 40%, preferably up to about 25%, and most preferably up to about 15%. After base treatment, the resin can be diluted, typically, with water.
For most high molecular weight resins the preferred treatment conditions convert greater than 90% of the aminochlorohydrin functionality to epoxide functionality, with less than a 10% reduction in the amount of azetidinium functionality. For some resins, especially ones with low molecular weight, it may be preferred to allow some or all of the epoxide functionality be consumed by crosslinking reactions. Less preferred treatment conditions are such that greater than 5 mole % of the azetidinium and/or epoxide is converted to glycol functionality. This conversion reduces the total amount of reactive functionality which, generally, reduces the effectiveness of the treated resin. To have a highly effective resin, the mole % hydrolysis of total reactive functionality (azetidinium, epoxide and/or aminochlorohydrin) to glycol is from about 0% up to about 20%, preferably up to about 10%, more preferably up to about 5% and most preferably up to about 2%. To have a highly effective resin, the level of azetidinium ion in the treated resin will be substantially unchanged compared to the level before treatment. In the context of the present invention this means that the treated resin will have at least about 80 mole % of the azetidinium functionality in the untreated resin, preferably about 90 mole %, more preferably about 95 mole % and most preferably about 100 mole %.
The wet strength effectiveness of the treated resin of the present invention will not be substantially lowered by the base treatment. In the context of the present invention this means that the treated resin will have at least about 80% of the effectiveness of the untreated resin, preferably at least about 95% and most preferably about 100%. With resins containing more than about 5 mole % of aminohalohydrin, the present invention may provide a treated resin with effectiveness greater than the untreated resin. The effectiveness improvement can be from about 2-50%, preferably the improvement would be greater than about 5% and most preferably greater than about 10%.
The treatment conditions for each resin can be optimized to a given set of conditions, however, one skilled in the art will recognize that other conditions will also give good results. For example, if a shorter reaction time is desired, then a higher temperature could be used with good results.
The treatment conditions can reduce the AOX content to less than 50%, preferably less than 25%, preferably less than 10%, preferably less than 5%, more preferably less than 1%, most preferably, less than 0.5% of the AOX content in the untreated resin on an equal solids level basis. Although the focus of the present invention is to reduce AOX, it can also be used to reduce the levels of the epichlorohydrin (epi) by-products, 1,3-dichloropropanol (1,3-DCP), 2,3-dichloropropanol (2,3-DCP) and 3-chloropropanediol (3-CPD), in polyaminopolyamide-epi resins or polyalkylene polyamine-epi resins. Additionally, the present invention could be used to convert 1,3-DCP and 2,3-DCP to epi. This epi could be removed from the resin by further treatment, for example, by distillation or extraction.
Gas chromatography (GC) was used to determine epi and epi by-products in the treated and untreated resins using the following method. The resin sample was absorbed onto an extrelut column (available from EM Science, Extrelut QE, Part #901003-1) and extracted by passing ethyl acetate through the column. A portion of the ethyl acetate solution was chromatographed on a wide-bore, capillary column. If the flame ionization detector was used, the components were quantitated using n-octanol as the internal standard. If an electrolytic conductivity (ELCD) detector or if the XSD detector was used, an external standard method using peak matching quantitation was employed. The data system was either a millennium 2010 or HP ChemStation. The FID detector was purchased from Hewlett-Packard (HP). The ELCD detector, Model 5220, was purchased from OI Analytical. The XSD detector was purchased from OI Analytical, Model 5360 XSD. The GC instrument used was a HP Model 5890 series II. The column was DB wax 30 mxc3x9753 mm with 1.5 micron film thickness. For the FID and ELCD, the carrier gas was helium with a flow rate of 10 mL/min. The oven program was 35xc2x0 C. for 7 minutes, followed by ramping at 8xc2x0 C./min to 200xc2x0 C. and holding at 200xc2x0 C. for 5 minutes. The FID used hydrogen at 30 mL/min and air at 400 mL/min at 250xc2x0 C. The ELCD used n-propanol as the electrolyte with an electrolyte flow rate setting of 50% with a reactor temperature or 900xc2x0 C. The XSD reactor was operated in an oxidative mode at 1100xc2x0 C. with a high purity air flow rate of 25 mL/min.
Kymene(copyright) ULX wet-strength resin is a polyaminopolyamide-epi resin available from Hercules Incorporated. The first sample used had a resin solids of 12.7% and a charge density of 3.36 meq/g at pH 1.8, 1.73 meq/g at pH 8 and 1.51 meq/g at pH 10. The second sample of Kymene(copyright) ULX wet strength resin used had a resin solids of 12.7% and a charge density of 3.28 meq/g at pH 1.8, 1.72 meq/g at pH 8 and 1.56 meq/g at pH 10.
E7045 wet-strength resin is a polyaminopolyamide-epi resin available from Hercules Incorporated. The sample used had a charge density of 3.34 meq/g at pH 1.8, 1.96 meq/g at pH 8 and 0.89 meq/g at pH 10 and a total solids of 13.0%.
Kymene(copyright) 557LX wet-strength resin is a polyaminopolyamide-epi resin available from Hercules Incorporated. It had a pH of 3.5, a total solids of 12.5%, and a Brookfield viscosity of 47 cps. It had a charge density of 1.39 meq/g at pH 10.
Kymene(copyright) 736 wet-strength resin is a polyalkylene polyamine-epi resin available from Hercules Incorporated. It had a pH of 3.3, a total solids of 37.8%, and a Brookfield viscosity of 250 cps. It had a charge density of 2.24 meq/g at pH 8.
Kymene(copyright) ULX2 wet-strength resin is a polyaminopolyamide-epi resin available from Hercules Incorporated.
The scope of this invention as claimed is not limited by the following examples, which are given merely by way of illustration. All parts and percentages are by weight unless otherwise indicated.